1. Field of the Invention
The present invention relates to a bellows pump which is a liquid transfer pump used particularly in industries of medicine, semiconductor, biotechnology, etc., and suitable for transferring high pure liquids.
2. Discussion of Background
Among the reciprocating pumps, the bellows pumps of such a type are employed in wider applications, because a relatively stable performance is assured with a light and simple construction. Particularly, a bellows which has a liquid-contact portion can be made from a heat- and corrosion-resistant plastics and hence, is most suitable even for transferring not only high purity liquid but also various corrosive liquids such as strong acids and strong alkalis.
FIG. 3 illustrates one example of such prior art bellows pumps.
The bellows pump shown in FIG. 3 comprises cylinder cases 2 and 3 horizontally placed within a housing 1 at a predetermined distace spaced apart from each other, bellows 4 and 5 made of a plastic material and contained within the cylinder cases 2 and 3 for lateral expansion and contraction, a rod 6 connected at its opposite ends to opposed end faces of the bellows 4 and 5, respectively, and gas pumping means 7 comprising a compressor and a solenoid valve for feeding a compressed gas alternately into the cylinder cases 2 and 3.
The bellows pump repeatingly produces the drawing and discharging of a liquid through access ports 8 and 9 provided in the bellows 4 and 5 by the bellows 4 and 5 alternately expanded and contracted by the action of the compressed gas fed through the gas pumping means 7. The provision of a check valve leading to the inlet and outlet ports 8 and 9 allows the liquid to be drawn and discharged in a given direction.
Now, in such prior art bellow pump, with a liquid having a higher temperature and a larger specific gravity, the bellows 4 and 5 are deformed due to the temperature and weight of the liquid during repeated use and as a result, a normal operation cannot be maintained. In addition, when the deformation of the bellows 4 and 5 is severe, the bellows 4 and 5 may sag into contact with inner wall of the cylinder cases 2 and 3 and to produce a rubbing.
Further, the prior art bellows pump is accompanied by the problem that because the bellows 4 and 5 are adapted to be laterally expanded and contracted, a gas is liable to be accumulated in the bellows 4 and 5, resulting in an unstable drawing and discharging forces and also in a degraded fixed delivery.
For an approach thereto, it is considered to provide a vertical bellows pump, but only the construction of the prior art bellows pump into a verical type cannot bring a basical solution to the problems, because the accumulation of the gas is produced in the lower one of the upper and lower bellows.